錳催化靛藍光度法快速測定水體中總氨方法之研究

Abstract

本文檢討以靛藍法測定水體中氨氮濃度的方法，以不同之分析角度嘗試將其改進之，包括: 酸鹼度之控制、反應速率、試劑之穩定度及保存。結果顯示，以酚為偶合劑、次氯酸為氧化劑、錳為催化劑，在適當的條件下，可使呈色反應時間大幅縮短，在常溫下反應可在三分鐘近乎完全(t99%<3min)。其關鍵條件在於其中間產物氯胺(chloramine)之反應須在pH 7-8的環境下生成，而生成後與酚之中間反應須先在pH 7.5-8.5 進行，最後再調到10.5使靛藍呈色。以錳為催化的機制使得試劑空白非常穩定，不會像使用nitroprusside為催化劑時有緩慢爬升的現象。雖然本文建議之方法所得靛藍的吸光係數較低(640nm=ca. 4500 M-1cm-1)，但其優勢為反應迅速，呈色後穩定，所有試劑都可以在配置後保存數月之久。本法以停流式自動分析法之偵測下限為0.5 uM ，在10 uM濃度之再現性(r.s.d.)約1 % (n=7) ，線性範圍可延伸至100 uM，每小時可分析15個樣本。本法適用於測定含高氨氮濃度之水體，如都市廢水、工業及農業排水，以及雨水、養殖池之監測等。

The indophenol blue method for the determination of dissolved ammonia has been reassessed in several analytical respects including pH control, reaction kinetics, choice of reagents and reagent stability. It was found that an optimal reaction rate (t99%<3 min at room temperature) can be achieved using phenol as the coupling agent, hypochlorite as the oxidant and manganese (II) as the catalyst. The key conditions are that the formation of the intermediate product-chloramine needs to form at pH 7-8, which further reacts with phenol at pH 8-8.5 and the final formation of the indophenol blue should be carried out at pH 10.5. The reagent blank of the proposed method is more stable than that of using dichloroisocyanurate and nitroprusside reagents. Even though the final molar extinction coefficient (640nm=4500 M-1cm-1) may be comparatively lower than that of traditional protocols, the present method takes advantages of being much faster, more consistent and all reagents can be stable for several months. The detection limit using a stop-flow automated device was 0.5 uM using 1 cm cell measured at 640 nm, and the precision was about 1% at 10 uM level with a linear range of up to 100 uM. The analysis throughput was 15 samples per hour. The method is suitable for the examination of high-ammonia-containing urban sewage, industrial and agricultural outflows as well as rain water and aquaculture pond water.